In the conventional type of electronic wristwatch having an alarm device, the alarm is mounted on or in the movement whereby the thickness of the watch is increased. Such construction is hence not applicable to thin type electronic wristwatches. Moreover, the movement of an electronic wristwatch is customarily sealed in a cavity in the watch casing so as to protect the movement against dirt and moisture. When the alarm device is mounted on or in a sealed movement, the sound of the alarm device is muffled so that it is not possible to obtain a loud alarm sound. If a loud alarm sound is wanted, the waterproof characteristics of the watch are impaired whereby the reliability of the watch is decreased. Furthermore, it is inconvenient to disassemble and assemble the watch for repair when the alarm device is incorporated with the movement.